Skin and clean the rabbits, then cut in pieces at the joints. Cover with cold water to which has been added the 4 tablespoons vinegar, and let stand overnight. When ready to cook, drain and dry well. Rub with salt, pepper and butter, place in a heavy baking pan, and place in a 400 degree oven for 15 minutes. Meanwhile, chop the onions fine and put in an iron skillet with 4 tablespoons melted butter. Brown lightly, add the flour and brown well. Add remaining ingredients, let simmer a few minutes, then add about 2 cups boiling water. Cook, stirring until smooth. Pour over the rabbits, return to the oven, bake slowly 20 minutes, basting frequently. Serve with cornbread.